Children's environmental health

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Coordination of new large-scale birth cohort studies

In the past 20 years, birth cohort studies to assess the risks to developing children from harmful chemicals in air, water and food have been undertaken in many countries. These birth cohort studies usually started during pregnancy and followed children through adolescence or beyond. Even the largest of these birth cohort studies, however, were not big enough to study rare outcomes such as childhood cancer or sudden infant death syndrome. To increase the sample size, investigators working with these older cohort studies are now making an effort to pool their data. Their efforts are hampered by the fact that the older studies did not usually agree upon disease outcome definitions, time periods of measurement, or methods for measuring biomarkers and chemical contaminants in air, water and food. This makes pooling data extremely difficult.

To avoid such problems in the next generation of large-scale birth cohort studies, it is worthwhile for investigators from various countries to invest time up front to agree on how to assess disease outcomes, measure biomarkers, and measure environmental exposures. Pooling of data, should that be desirable, with then be much more straightforward.

To strengthen, international cooperation on the next generation of birth cohort studies of child health and the environment, WHO is willing to work with others towards defining a list of core elements for inclusion in birth cohort studies. Such core elements could include disease outcome measurements, biomarkers and exposure measurements. This will help to move the science forward by increasing the likelihood that datasets can be easily combined in the future, yielding studies with more power to identify positive results.

There is currently a unique window of opportunity to make significant progress because a number of birth cohort studies are either being designed or in the early stages of being launched. During this unique time, it may be possible to achieve agreement on a number of important study elements.